This invention relates generally to transformers and more particularly, but not by way of limitation, to transformers in which capacitively and magnetically coupled voltage transients, such as voltage surges created by lightning striking power distribution lines, are filtered so that the transients do not damage a load powered through the transformer. The present invention also pertains to transformers which improve the power factor for an inductive load.
In the oil and gas industry, electric motors are used to drive submersible pumps which are located down in an oil or gas well. Such a motor is typically energized through a transformer connected at the well site to a conventional power distribution network.
One problem which has arisen in this system is that voltage transients in the power distribution network can be communicated through the transformer to the motor. When large enough or of long enough duration, these transients can damage the motor. This type of problem can arise such as when lightning strikes one or more of the primary distribution lines in the network or such as when some type of switching occurs in the network.
A typical transformer to which such transients can be conducted typically includes a primary winding connected to the power distribution network and a secondary winding connected to the motor (or other load). The primary and secondary windings are physically distinct, but they are typically spatially close to each other and they are inductively coupled. This permits transients received by the primary winding to be either capacitively coupled or magnetically coupled into the secondary winding through which they would then be applied to the load. Thus, to solve this transient problem, there is the need for a transformer that does not transmit, or at least reduces the transmission, into the secondary winding of either capacitively coupled transients or magnetically coupled transients.
Another shortcoming of the downhole submersible pump system, and more generally a shortcoming of at least induction motor systems, is that induction motors operate at less than unity power factor. Increasing the power factor would lower the primary system load and the transformer load. This could produce cost savings in otherwise needed transformer core, coil and cooling surface construction. Thus, there is also the need for a transformer which improves the power factor of an inductive load system such as one including an induction motor.